Various light-emitting devices using a polymer as a light-emitting material (polymer LEDs) have been studied.
As a method for forming a light-emitting layer of a polymer LED, a forming method by an inkjet method using a solution composition containing a polymer and a solvent has an advantage of enabling production of a light-emitting device of large area at low cost.
As solution compositions applicable to such inkjet method, for example, a solution composition containing a polyfluorene derivative and a solvent (WO00/59267 pamphlet) and a solution composition containing polyarylenevinylenes and a solvent (WO02/96970 pamphlet, Kokai (Japan unexamined patent publication) No. 2000-323276) are known.
However, when forming a light-emitting layer with by an inkjet method using a solution composition, if the viscosity of the solution composition is too low, this causes a problem that a film having high uniformity is hardly obtainable. Therefore, a solution composition having high viscosity is desired.
Furthermore, according to restrictions other than the viscosity, the solution composition is required for keeping the polymer concentration thereof within a specific range and having high viscosity; to meet this requirement, the conventional solution compositions are responding by selecting the kind of the solvent depending on the kind of the polymer.